Not only Hartz will kill your cat, but many others will kill it. Sergeants flea drops can also kill your pet. My mom put the drops on my cat, and later on he was having seizures. My mom thought he was just acting crazy when the dog chased him up the couch and upset him. He was moving so fast across the floor, so I am guessing it was from the medicine. I woke up later that night to the sound of a noise like someone choking. My cat was on the floor running around in circles. I picked him up and he started trying to grab hold of me, and slightly clawed me up in the process. Once I got him to calm down, he suddenly snapped out of it, took a few steps, meowed as though he did not no what happened. He was under my bed making a hacking noise, so I decided to go somewhere else to sleep. I woke up with my brother screaming and crying. The cat was having seizures again, only this time it was even worse. He was chomping his mouth open and shut over and over and over. We wrapped him in a towel, and put a plastic medicine dropper in his mouth to keep him from destroying his tounge. We figured out right away that it was the flea drops. After what was probably a long time, he suddenly stopped, puked up some fluids, gagged again, and then he dropped dead. My mom was in so much denial about using the medicine she was so bad off she didn’t want to live any more. I am just writing this to make sure all others do not make the same mistake as we did.